1. Field of the Invention
The present invention relates to aerodynamic devices and, more particularly, is directed towards aerodynamic devices for sails.
2. Description of the Prior Art
The force which drives a sailboat to windward is similar to the force which gives lift to a glider's wing. The airfoil characteristics of a sail is achieved by building a fore-to-aft parabolic curve into the sail. The curvature is greatest near the luff or forward edge of the sail and becomes straighter near the leech, or after edge of the sail. When a boat reaches to windward, air flows around the sails from luff to leech. As the wind meets the luff, it splits to form a windward airflow and a leeward airflow. The molecules of air on the leeward side have a greater distance to travel around the sail than the molecules of air on the windward side. The speed of the leeward air flow is greater than the speed of the windward air flow. As a result of this difference between windward and leeward airflow speeds, the pressure is lower on the leeward side of the sail and a suction pull is created which draws the boat forward.
Addition of a jib in close proximity to the mainsail has a considerable influence on windflow. A correctly trimmed jib set ahead of the mainsail creates a narrow slot between the jib's leech and the mainsail's luff which acts as a venturi to accelerate the leeward airflow and to lower the pressure at the leeward side of the mainsail. In consequence, the suction pull on the mainsail is increased.